Teacher's notes and answers to questions in the book - Hodder Plus ...

WJEC GCSE Additional Science Teacher’s Notes
Ionic compounds in Question 11:
a lithium chloride, LiCl 16.5 % lithium, 83.5 % chlorine
b potassium oxide, K 2 O 83 % potassium, 17 % oxygen
c sodium sulfide, Na 2 S 59 % sodium, 41 % sulfur
d magnesium carbonate, MgCO 3 28.6 % magnesium, 14.3 % carbon, 57.1 % oxygen
e calcium nitrate, Ca(NO 3 ) 2 24.4 % calcium, 17.1 % nitrogen, 58.5 % oxygen
f beryllium oxide, BeO 36 % beryllium, 64 % oxygen
g rubidium carbonate, Rb 2 CO 3 73.9 % rubidium, 5.2 % carbon, 20.9 % oxygen
h ammonium sulfate, (NH 4 ) 2 SO 4 21.2 % nitrogen, 6.1 % hydrogen, 24.2% sulfur, 48.5 %
oxygen
13. Calculate the total mass of reactants and products in the following reactions:
a N 2 (g) + 3H 2 (g) → 2NH 3 (g)
Reactants: (2 × 14) + 3 × (2 × 1) = 34
Products: 2 × (14 + (3 × 1)) = 34
b 2H 2 (g) + O 2 (g) → 2H 2 O (g)
c
Reactants: 2 × (2 × 1) + (2 × 16) = 36
Products: 2 × ((2 × 1) + 16) = 36
Mg (s) + H 2 SO 4 (aq) → MgSO 4 (aq) + H 2 O (g)
Reactants: 24 + ((2 × 1) + 32 + (4 × 16)) = 122
Products: (24 + 32 + (4 × 16)) + (2 × 1) = 122
d NaOH (aq) + HNO 3 (aq) → NaNO 3 (aq) + H 2 (l)
Reactants: (23 + 16 + 1) + (1 + 14 + (3 × 16)) = 103
Products: (23 + 14 + (3 × 16) + ((2 × 1) +16) = 103
14. Calculate the mass of calcium oxide formed by the complete decomposition of 5 kg of calcium
carbonate.
CaCO 3 (s) → CaO (s) + CO 2 (g)
Relative formula mass of calcium carbonate = 40 + 12 + (3 × 16) = 100
Relative formula mass of calcium oxide = 40 + 16 = 56
So 100 g of calcium carbonate makes 56 g of calcium oxide
1 g of calcium carbonate makes (56/100) = 0.56 g of calcium oxide
5 kg = 5000 g of calcium carbonate makes 5000 × 0.56 = 2800 g of calcium oxide = 2.8 kg
15. Calculate the mass of sodium chloride that can be formed from the neutralisation of 8 kg of sodium
hydroxide with hydrochloric acid.
NaOH (aq) + HCl (aq) → NaCl (aq) + H 2 O (l)
Relative formula mass of sodium hydroxide = 23 + 16 + 1 = 40
Relative formula mass of sodium chloride = 23 + 35 = 58
So 40 g of sodium hydroxide makes 58 g of sodium chloride
1 g of sodium hydroxide makes (58/40) = 1.45 g of sodium chloride
8 g of sodium hydroxide makes 8 x 1.45 = 11.6 g of sodium chloride
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